Analysis: carbon capture looks really, really expensive

If we can't get our current emissions under control, is it possible to remove …

Carbon capture and storage (CCS) has mostly received attention as a way to limit the impact of burning coal, which emits the most CO2 of all fossil fuels. Using this approach, CO2 would be captured from the exhaust stream of a power plant and pumped into a geological formation that would store it for centuries, preventing it from influencing the climate or ocean chemistry. As emissions continue to rise, CCS has attracted attention as a way to emit now and fix the problem later. The same technology that isolates CO2 from the exhaust stream of a power plant could also conceivably pull it right out of the atmosphere.

But how much does it cost? Some initial estimates put the cost of CCS from the atmosphere at under $200 per ton. But a new analysis in PNAS suggests these estimates are misguided—we already know how much it costs to obtain trace chemicals from a mixture, and it's a whole lot more expensive than that.

The PNAS authors focus on two things: a thermodynamic analysis of CCS, and an empirical evaluation based on our experience with industrial processes for isolating trace gasses.

The thermodynamic analysis is easy to understand. We can calculate the energetic cost of taking gas with our current level of CO2 (about 400 parts-per-million) and cutting that level in half, while concentrating what we've removed. It's only about 20 kiloJoules for each mole of CO2.

But nothing ever actually approaches that sort of perfect efficiency. For example, the authors note that NOx emissions are removed from the exhaust gasses of power plants through a chemical reaction that's energetically favorable. But the energetic costs of setting up the reaction components and moving them and the exhaust gasses through the system is huge. As a result, nearly 500kJ of energy is expended for each mole of NOx removed.

Unfortunately, thermodynamics can only set a lower limit on the amount of energy (and thus cost) that CCS will require. It doesn't provide any guidance as to how much more the actual cost will be and, right now, we've only got information from small-scale research systems.

But there are non-thermodynamic methods of estimating these costs. The authors point out that, back in 1959, someone named Thomas K. Sherwood analyzed the empirical relationship between the market price of a metal and the metal's concentration in the ore that we obtain it from. Since then, Sherwood's methods have been adapted for things like isolating pollutants from a waste stream, obtaining valuable organic compounds, and (most importantly) obtaining a single gas from a complex mixture.

Here, things look pretty good when it comes to going after the exhaust from power plants. The high concentration of CO2 means that it would only cost about $10/ton for coal-fired planets and $25/ton for natural gas. The atmospheric concentration, however, is over 100 times lower, which shoots the cost up to $2,500/ton. Even adding in various optimistic assumptions doesn't bring the cost down below $1,000/ton.

At those levels, CCS from the atmosphere just doesn't make sense. "Unless a technological breakthrough that departs from humankind’s accumulated experience with dilute gas separation can be shown to 'break' the Sherwood plot and the second-law efficiency plot," the authors conclude, "direct air capture is unlikely to be cost competitive with CO2 capture at power plants and other large point sources."

The authors have identified one potential way to "cheat." Biomass can sometimes be obtained cheaply, and could be burned in place of fossil fuels in a plant with CCS equipment. That way, biology does the hard part of extracting carbon from the atmosphere, which we then capture when it's economical, as part of a high-concentration exhaust stream. Right now, however, we haven't done biomass power on the sorts of scales needed to really know if this is viable.

In any case, other researchers have come up with numbers that are substantially lower than these for atmospheric CCS. Hopefully, they'll put together a response to this paper.

I take the doomer view of global warming. We can all agree it's happening and it's man's fault (the science is clear on that), but It's going to be impossible to convince people that it's actually happening, let alone get them to do anything about it when entrenched interests would have to give up some profit for a long term change decades from now. Business doesn't care about the long term. Executives get promoted for improving profit in the next quarter, not the 100th quarter from now.

The world is going to hell. The only thing we can do is sit back and watch it burn.

It seems to me if they want to capture and store carbon, they need to figure out how to make it into a solid. Graphite, nano-tubes, diamonds! But we probably don't know how to do that, or it would take too much energy and release more carbon than it takes back. But you know what does know how to do this? nature.

I think the biomass thing sounds like the best bet. I always thought bamboo sounded like a good choice. It grows crazy fast, and is useful as a material to make stuff.

Granted, I have no expertise to back up these fleeting ideas, so I am sure I am missing some key bit of info that renders this idea worthless, but that's OK.

For low energy atmospheric CO2 recovery, Dr David Keith is doing some interesting work. It's definitely not a hugely promising area of study, but Dr Keith gets a lot of respect in the CCS community. Very smart guy.

I've done engineering studies on implementing CCS on combustion systems, and the costs being advertised above are still a bit of a pipe dream. Like anything that hasn't been commercialized before, it's going to be quite expensive before it gets any cheaper.

If you want to do solvent contacting for removal, you need to circulate enormous amounts of solvent to get good removal at near atmospheric pressures. Most of the equipment is so big it is a step change away from what we would currently use for SOx removal.

Oxyfuel combustion is promising in that it gives you a much CO2 richer exhaust stream because you are combusting on pure O2 without the dilution of N2. Problem is the burners don't really exist and the exhaust gas recirculation for temperature moderation needs to be perfected. Plus O2 plants are expensive and very energy intensive.

Final problem is purification and compression of the final CO2 product. Again huge horsepower required for taking the relatively low pressure CO2 up to supercritical for transport.

As far as risk, I am far less worried about storage formations catastrophically leaking than I am a pipeline rupturing. If you live in a valley and one of these is nearby, I'd move.

Biomass capture is the best form anyway, regardless of whether you then burn it for energy and extract from the waste.

Trees are probably THE best carbon capture device on the planet. Solar powered, self propogating, "free", and hydrate the surface air. Moderate-term storage, with a certain percentage going to long term storage due to decay into ground products.

Unfortunately, they also seem to be the enemy of modern man. :-D Until we do something similar ("non-earth" energy: use solar power, tidal, etc), we're always going to spend more energy to capture the carbon than we get, raising the cost of the effort, or merely trading one waste product for another. It costs energy to tuck this stuff away, and that's got to come from somewhere. The carbon is airborne because it is energetically favorable to do so, it's not going to suddenly come out of that form. Something has to spend energy to put it back, and the only way we can do that without making things worse is to use incoming energy.

It just so happens that trees figured out how to do it far better than we have.

It seems to me if they want to capture and store carbon, they need to figure out how to make it into a solid. Graphite, nano-tubes, diamonds! But we probably don't know how to do that, or it would take too much energy and release more carbon than it takes back.

I agree, but I just want to point out for fun that we do know how to precipitate diamond. It works well, though probably not at atmospheric levels of CO2. It also is not energetically favorable.

...and if they want to sequester that plant material for a long time, then stop recycling paper and bury it.

Not only will it be insanely cheaper than current gaseous CO2 sequestration, it will be predictably stable for hundreds or thousands of years with zero intervention, and if there is a leak, we can call it confetti...

Trees are probably THE best carbon capture device on the planet. Solar powered, self propogating, "free", and hydrate the surface air. Moderate-term storage, with a certain percentage going to long term storage due to decay into ground products.

You know, I've wondered if we wouldn't be better off from a carbon standpoint by not recycling paper, but deliberately landfilling it. We grow a massive amount of biomass specifically for that purpose; by recycling less, we incentivize more biomass production and sequestration, that we get to use profitably in the process.

Trees are probably THE best carbon capture device on the planet. Solar powered, self propogating, "free", and hydrate the surface air. Moderate-term storage, with a certain percentage going to long term storage due to decay into ground products.

You know, I've wondered if we wouldn't be better off from a carbon standpoint by not recycling paper, but deliberately landfilling it. We grow a massive amount of biomass specifically for that purpose; by recycling less, we incentivize more biomass production and sequestration, that we get to use profitably in the process.

I read somewhere that coal reserves are the equivalent of covering he entire planet with trees 25 times. I think it's a better solution than most though - we should go back to burning wood for fuel and bury all the charcoal remains. In 300 million years when the monkeys are in charge they can have something to burn then.

Trees are probably THE best carbon capture device on the planet. Solar powered, self propogating, "free", and hydrate the surface air. Moderate-term storage, with a certain percentage going to long term storage due to decay into ground products.

You know, I've wondered if we wouldn't be better off from a carbon standpoint by not recycling paper, but deliberately landfilling it. We grow a massive amount of biomass specifically for that purpose; by recycling less, we incentivize more biomass production and sequestration, that we get to use profitably in the process.

Actually, your C. sativa (hemp) plant is one of the faster biomass plants, not trees, although I think bamboo is right up there as well. Still, I vote for either making a nuclear power plant for every coal plant to convert the coal CO2 into a stable form to bury, or my preferred method, start raising dinosaurs and bury them in mass graves for future fossil fuels.

I had watched a how it's made show more than a few years ago where only one of the beer companies was selling almost pure CO2 for dry ice production on the scale of 10's of tons dry ice per a day. And, dry ice wastes a large amount for the cooling process.

If they want high concentrations, why not just capture the almost pure CO2 from fermentation? I realize the tv show was a few years old, but at the time, the rest of the breweries were just venting it off.

Hemp, kenaf, or switch grass sound good for biological capture, but given that CO2 has a relatively high freezing point, compared to other atmospheric gases, would not that be a relativley simple way to separate CO2 from the rest of the atmosphere?

Hemp, kenaf, or switch grass sound good for biological capture, but given that CO2 has a relatively high freezing point, compared to other atmospheric gases, would not that be a relativley simple way to separate CO2 from the rest of the atmosphere?

just chill

On the one hand, I think that the level of atmospheric CO2 is so low (yes, low) that to extract any sizeable quantity, you would have to cool an enormous volume of air. So much as to be impractical, and bumps into the "yeah, but it took energy to do that... and thus put more in than it took out". However, I also recall reading that as the surface warms, the upper atmosphere cools (which, I think, is also why weather gets more extreme, not just hotter) so this may reach a point where it is self-solving.

Trees are really good at sucking carbon out of the atmosphere. And where their biomass becomes trapped in underground geological formations, the resulting heat and pressure converts it to... coal.

So I think we're looking at this problem the wrong way. Coal is an excellent way to store carbon. All we have to do is leave it in the ground where we found it. Anything else would be over-thinking the problem.

If there were only some sort of natural mechanism that could capture carbon from the atmosphere using energy from the sun...

Hey, yeah! Make them self replicating so it would spread over the undeveloped portions of the planet! Just for kicks, let's pretend it would break up CO2 into free oxygen we could breathe! And while we're fantasizing, it would turn all that nasty carbon into,,,get this,,,SUGAR!!!! I know, I know, crazy, nutty, but there you are.

Even if you accept that the climate has been anything but amazingly stable, if you discount the medieval warm period as some sort of a fluke, if you further accept that human activity is to blame, the biggest leap of all is that we can actually do something about it. Billions of homes need heating, cars need fuel, appliances need electricity and the one reliable means of generating clean electricity (nuclear) has been demonized to the point of unacceptability.

So unless people can somehow be convinced to give up cars, home heating/cooling and electricity, carbon emissions are here to stay, particularly since China and India will be the largest emitters in the 21st century and thus far have shown absolutely no inclination to reduce emissions.

Of course, people will continue to piss and moan but why is there no real "green" movement instead of happy talk? Because at heart the greens are hypocrites of the worst sort.

If there were only some sort of natural mechanism that could capture carbon from the atmosphere using energy from the sun...

Hey, yeah! Make them self replicating so it would spread over the undeveloped portions of the planet! Just for kicks, let's pretend it would break up CO2 into free oxygen we could breathe! And while we're fantasizing, it would turn all that nasty carbon into,,,get this,,,SUGAR!!!! I know, I know, crazy, nutty, but there you are.

Even if you accept that the climate has been anything but amazingly stable, if you discount the medieval warm period as some sort of a fluke, if you further accept that human activity is to blame, the biggest leap of all is that we can actually do something about it. Billions of homes need heating, cars need fuel, appliances need electricity and the one reliable means of generating clean electricity (nuclear) has been demonized to the point of unacceptability.

So unless people can somehow be convinced to give up cars, home heating/cooling and electricity, carbon emissions are here to stay, particularly since China and India will be the largest emitters in the 21st century and thus far have shown absolutely no inclination to reduce emissions.

Of course, people will continue to piss and moan but why is there no real "green" movement instead of happy talk? Because at heart the greens are hypocrites of the worst sort.

Thank you for a post consisting of nothing but unsupported assertions.

The authors have identified one potential way to "cheat." Biomass can sometimes be obtained cheaply, and could be burned in place of fossil fuels in a plant with CCS equipment. That way, biology does the hard part of extracting carbon from the atmosphere, which we then capture when it's economical, as part of a high-concentration exhaust stream. Right now, however, we haven't done biomass power on the sorts of scales needed to really know if this is viable.

Global warming is a lie.

Okay, now that's out the way, they could use yard and agricultural waste pretty easily to do this.

But I really don't understand why the green conspiracy wants all this CO2.

Are you guys building tons of high-powered lasers to take over the world or something?

No, not that. Recycling the paper and burying the trees would use less energy, and hence produce less CO2. You could, of course, build stuff from the trees, but you'd want to make sure that whatever you build doesn't catch fire.

Shouldn't it be title, "Carbon Capture from the atmosphere is expensive"?

YES! Please fix the title of the article. As it stands it's incredibly confusing -- only in the 3rd from last paragraph do you state that they are talking about concentrating CO2 from the atmosphere . Which is a clearly dumb idea to start with, because of the 400ppm issue. I wasn't even aware that anyone was proposing it!

As the authors say, "direct air capture is unlikely to be cost competitive with CO2 capture at power plants and other large point sources."This is obvious in my book - it's cheaper to start with a source that is 30% CO2 than one that is 400 ppm. A more interesting analysis might be "is it worth getting rid of the N2 in the exhaust stream, or just sequester all of it?'

I appreciate that everyone is gung-ho about reforestation as a carbon sequestration system, but there's simply not enough land for that. Freeman Dyson suggested using genetically-engineered super-trees that we could design to capture more carbon, but that's simply not feasible unless they can "drop diamonds instead of leaves" as David Archer put it. Where would you even plant them? We can't give up arable farm land, and we can't replace the diversity of natural trees for a planet-wide clone farm and expect to come out ahead. Speaking of arable land, trees take up and sequester far more than just carbon: they take nutrients out of the soil. Planting a bunch of trees just to bury them in old mines or salt domes will worsen soil erosion and depletion, which are already problems in themselves. The amount of CO2 emissions we're talking about are simply too massive to solve it with just trees.

Recent paper that attempts to account for and remove the variable effects (volcanoes, ENSO, solar irradiance variability, etc) from the temperature measurements to provide a better assessment of the true global warming rate.

I'm not following this sudden enthusiasm for biomass as a way to extract all that excess CO2.

Sure, using biomass as a source of fuel makes sense (assuming we can get enough to help). The CO2 gets converted into biomass, the biomass gets converted into CO2 again, gets converted into biomass again -- it makes for a lovely little loop that doesn't add "new" carbon into the system. No net increase in atmospheric CO2. Fantastic.

But it doesn't appear to do much, if anything, to compensate for the tons of "fossil" carbon we're re-introducing into the loop. While that switch grass or hemp or tree is growing, it takes a little CO2 out of the atmosphere, but as soon as we burn it, that CO2 returns to the atmosphere. If we landfill it, directly or in some alter form (eg. paper) it decomposes, and this adds not only CO2, but also (admittedly much shorter lived but far more powerful) greenhouse gases such as methane.

It would allow us to reduce our boosting of current CO2 levels (ie. reduce our re-introduction of carbon previously isolated by large-scale but slow natural geological mechanisms) but it won't do much about the excess fossil carbon we have already reintroduced and continue to re-introduce from geological deposits.

It strikes me as a classic non-solution: too little, too late, and very temporary in any case.

But I really don't understand why the green conspiracy wants all this CO2.

It depends on who you are talking about specifically.

The 'extremist environmentalists' like harping on CO2 because reducing CO2 can only be done by reducing human activity and industry. Which is the ultimate goal. To them human activity and progress is a cancer on the face of the Earth. Anything to reduce the impact is a good thing and going after CO2 emissions fits perfectly with their agenda.

The government types like it because it is used as a excuse to gain more political power and money. Every industry on earth generates CO2. You, literally, cannot do anything without generating more CO2. It's impossible. So they can use this as a excuse to put more pressure and exert more influence on any target they feel like. This creates great opportunity to garner political favors, power and increases the amount of money making opportunities you can get by being a professional politician.

The 'extremist environmentalists' like harping on CO2 because reducing CO2 can only be done by reducing human activity and industry. Which is the ultimate goal. To them human activity and progress is a cancer on the face of the Earth. Anything to reduce the impact is a good thing and going after CO2 emissions fits perfectly with their agenda.

Meanwhile most people would rather have a world with less pollution and ecological stress while still maintaining high levels of technological sophistication and living standards, which is easily achievable compared to the current status quo (the bar, after all, is very low).

Quote:

The government types like it because it is used as a excuse to gain more political power and money. Every industry on earth generates CO2. You, literally, cannot do anything without generating more CO2. It's impossible.

We can, however, switch to less carbon-intensive sources of energy that also don't involve depleting increasingly scarce hydrocarbon resources in a blind dash to fuel crash, leaving our descendants with drastically fewer chemical riches to exploit and a severely altered environment.

I somehow sense that you're not really looking at the entire picture here, perhaps even pointing us to one you've made out of straw.

CCS is just a bad idea. It doesn't fix the problem it just sweeps it under the rug. Can't wait for the first "oopsie" when a whole pile of people die to a CO2 leak from storage.

This

Holding on to a gas in mega-ton quantities forever is going to be a lot more difficult than nuclear waste disposal. A lot harder to find storage sites, too. Nobody will want that stuff anywhere near them.

The reason millions are going into research is avoid any oopsie. Oil and gas pockets are have been stored in geologic formations for millions of years.

One of the more interesting things about buildings in downtown Los Angeles is that if they are in certain areas (the methane zones) they have to have gas detectors or some kind of mitigation system in place. Before that code requirement, warehouses would sometimes explode when natural gas - leaking from those geological formations you mentioned - accumulated and got touched off by a stray spark.

We can, however, switch to less carbon-intensive sources of energy that also don't involve depleting increasingly scarce hydrocarbon resources in a blind dash to fuel crash, leaving our descendants with drastically fewer chemical riches to exploit and a severely altered environment.

I somehow sense that you're not really looking at the entire picture here, perhaps even pointing us to one you've made out of straw.

It will take lots and lots of energy to make the switch though. Oh, and really big batteries (that we don't know how to make) for the cloudy and/or windless days. Or did you have something else in mind?